The exemplary embodiment relates to printing systems. In particular, it relates to a developer homogenizer which reduces variations between the developer material supplied to different marking engines.
In typical xerographic printing devices, such as copy machines and laser beam printers, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developer material. Generally, the developer material, which comprises toner particles adhering triboelectrically to carrier granules, is supplied from a development housing. The latent image attracts the toner particles from the carrier granules to form a toner powder image. The developed image is subsequently transferred to the print medium, such as a sheet of paper. The fusing of the toner image onto paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure.
The carrier granules remain in the development housing while the toner particles are consumed in the forming of images. Fresh toner is generally supplied to the development housing from a replaceable storage bottle. Over time, the carrier granules can age through repeated circulation in the housing. To compensate for this, some development housings progressively discharge a portion of the developer as waste. A small amount of fresh carrier material is incorporated in each fresh toner bottle to compensate for the carrier granules lost in this process.
In multi-engine printing systems, particularly those employing color marking engines, it is desirable for the image quality from each marking engine to be the same, or as close to that of the others as possible. Otherwise, documents which include pages produced by different color marking engines can have noticeable page to page differences. For example, in some applications one marking engine may be used to print side 1 of a duplex sheet and the second marking engine will print side 2. If the output print quality of the first marking engine is different from the second engine, this difference can lead to unacceptable performance. One strategy for mitigating these differences is to monitor the output print quality from each engine with a sensor, such as a full width image bar, compare the two different print quality outputs, and then select the halftone exposure to bring the print quality more in line with each other.
While each marking engine tries to control itself to a common mass developability, in doing so, it can end up working at different image, background, and bias levels, which in turn tends to result in subtle, but other print quality defects. While some image quality consistency problems can be resolved through careful selection of tone reproduction curves, halftone selection, and control of process parameters, differences in image quality may still exist.
There remains a need for improvements in image quality and consistency for multi-engine printing systems.